In the art, there are several devices and methods using electrofusion for pipes joints. For instance, the U.S. Pat. No. 7,144,045 relates to an electrofusion joint assembly that includes a meltable part, such as the pipe itself or an intermediate part, and a heating element secured to the pipe. Fasteners are used to secure the heating element which is connected to an external power source.
Another example is the U.S. Pat. No. 6,680,464 that relates to an electrofusion pipe joining control device, wherein the pipes are preferably made of thermoplastic material. It includes a coupling and an arrangement for securing the coupling to the pipes and, at the same time, it defines an electrofusion fusible seal.
Furthermore, the U.S. Pat. No. 6,375,226 relates to a multilayer thermoplastic pipe connector with a hollow tubular coating capable of receiving pipes, elements to create thermal fusion, mechanical fastening elements and sealing elements.
U.S. Pat. No. 6,127,662 relates to a device and method to join a first plastic pipe to a second pipe, which material does not bond properly to the first pipe material, and uses an electrofusion sleeve of a plastic material which bonds properly to the first plastic pipe and includes a first heating coil in contact with the first pipe and a second heating coil in contact with the second pipe. Such sleeve includes, at one end, linking material capable of producing a good bond between the second pipe and the sleeve material.
By way of example, it is worth mentioning the device described in the U.S. Pat. No. 5,798,021; the pipe union system in the U.S. Pat. No. 5,127,116; the electrofusion joints in the U.S. Pat. Nos. 5,116,082 and 4,929,817; or the electrofusion joint mentioned in the Japanese Patent number JP8240295 (A).
None of these patents actually solve the problem of steel pipeline joint coating for lightly-thick anticorrosive coating and for highly-thick thermal coating.
We will introduce a short explanation of the most usual cases found in the art and each of their problems as follows:
1) Lightly-thick anticorrosive coatings: In this case, materials and methods that have satisfactory properties with regard to its bond to the steel surface of the pipes are used. However, in the “overlapping” area using the original coating of said pipes, the best bond levels will not be enough to avoid considering it a critical area causing recurrent failures.
2) Highly-thick coating for pipe thermal insulation: The external coating of steel pipes used for transporting petroleum hydrocarbons in offshore areas using highly-thick polyolefin materials (polypropylene) insulates them, thus maintaining ideal temperature levels which are needed to comply with the conditions related to the flow systems inside.
There is evidence that, up to the moment, an appropriate solution has not been found for joint coating between pipes to guarantee a perfect bond in the interface created by the material used to coat the joint and the coating of the external surface of the pipes.
The materials used at present have different origins, characteristics and associated problems. These can be considered as:
a) Not having polyolefin origin: These materials, in general, do not have the same insulation level as the polypropylene and this is not recommended.
On the other hand, it may not be possible to obtain satisfactory bond levels to the surface of the original coating by using these materials.
In general, elastomeric polyurethanes are used. Even if the application method is fast and does not present major problems, its main disadvantage arises from the limited or almost null bond level to the original polypropylene of the pipes. This does not allow a good water resistant seal, specifically in great depths where hydrostatic pressure obtains considerable values. Therefore, this is not an acceptable solution for most users.
b) Having polyolefin origin: Its application has serious difficulties. It requires a great amount of material mass (related to the coating thickness) applied to high temperature, demanding an excessive cooling period (considered as the difference between the melting temperature and the room temperature). Also, it presents evident problems of contraction and termination. This critical system of mass, temperature, cooling time and contraction create the environment of unfeasibility for its use as an on board ship reference system in offshore area.
By means of the invention, two definitely unique purposes can be achieved:
using, for the joint coatings, the same kind of polyolefin material placed previously in the original coating of the pipes, thus stopping the creation of an interface common among systems where the components are chemically incompatible; and
just a small amount of the mass is the one to be heated in order to create a perfect bond between the original coating (already placed in the pipe) and the new one (originated from the joints), definitely establishing a method of unique characteristics that takes into account its safety, a quick performance and equipment simplicity.